1. Field of the Invention
The invention is based on a pump unit with a needle bearing particularly useful as a pump for traction controlled hydraulic vehicle brake systems.
2. Description of the Prior Art
A pump unit with a needle bearing of this generic type is already known (German Patent 197 20 615 C1). The pump unit has an electric drive motor, whose shaft engages an eccentrically embodied sleeve of a component in such a way as to transmit torque. The sleeve is supported with a respective roller bearing, toward the motor and remote from the motor, in a pump block onto which the motor is also mounted. Immediately adjacent the roller bearing toward the motor, the sleeve carries a needle bearing. The sleeve acts as an inner race of the needle bearing, whose needles received in a cage carry a needle bush as an outer race. The outer race is engaged by pump pistons, which are received radially to the axis of the motor shaft in the pump block.
Needle bearings with an inner race are not self-locking. The outer race of the known needle bearing is therefore provided, on both of its two face ends, with a respective radially inward-oriented rim, and these rims fit over the needles on the face end. To assure the axial position of the needles and outer race on the inner race, one rim of the outer race is intended for engagement, with play, of the end face of the inner race of the roller bearing toward the motor. Conversely, on the side of the roller bearing remote from the motor, a collar formed onto the eccentric sleeve is embodied for the other rim of the outer race to run up against. However, because of this design there are disadvantages: Because of the collar, the two roller bearings are relatively widely spaced apart, and the collar requires expensive machining or deformation of the component that has the sleeve. Since the rim of the needle bush toward the motor is embodied as completely flat on the face end, there is furthermore the risk that it will cause damage, in wear-caused contact with a bearing cover disk of the roller bearing toward the motor.
From German Patent Disclosure DE 44 33 972 A1, in a pump unit, it is known to embody one end portion of a motor shaft as an eccentric element, on which the needles of a needle bearing roll directly. The outer race, which is engaged by a pump piston of a radial piston pump, has one rim, fitting over the needles, on each of the two face ends. The outer race is braced on the inner race of an immediately adjacent roller bearing of the motor shaft by one rim; the other rim is assigned a stop face on a shoulder of a bore in a pump block, in order to support the needle bearing axially. In this embodiment, it is disadvantageous that the stop face has to be treated to reduce wear, which is complicated.
Furthermore, from European Patent Disclosure EP 0 637 690 A1, in a pump unit with a radial piston pump, it is also known to press an eccentric sleeve onto a motor shaft, which in turn imposes a press fit on a roller bearing embodied as a radial deep groove ball bearing, whose outer race is engaged by a pump piston. Since such a roller bearing is self-locking, no provisions are needed to secure the axial position of its outer race.
The pump unit of the invention is advantageous in terms of the fact that with little effort or expense, self-locking of the needle bearing on the shaft of the drive motor is attained by providing that the outer race is guided by form locking of its rim, between the two inner races, secured to the shaft with force locking, of the needle bearing and the roller bearing. No other guide element or stop face for the outer race is needed, which has not only cost advantages but leads to an axial shortening of the entire arrangement, which in turn then makes a compact, economical design of the pump block possible. Moreover, because of the design of the inner race of the needle bearing as an eccentric element, the manufacture of the motor shaft becomes less expensive, and high bending strength of the shaft is obtained.
In one embodiment of the invention, a specific relation exists in terms of the area between the rim of the outer race of the needle bearing and the inner race of the roller bearing. The offset bend or protuberance prevents the rim from running up against a bearing cover disk of the roller bearing as well as preventing wear to it. The offset bend or protuberance makes a volume of material available that can decrease over the service life of the pump unit as a result of wear. This prevents damage to the needle bearing or roller bearing. Moreover, because of the design of the inner race of the needle bearing as an eccentric element, the manufacture of the motor shaft becomes less expensive, and high bending strength of the shaft is obtained.
By the provision recited in claim 3, a contact defined in terms of area between the rim of the outer race of the needle bearing and the inner race of the roller bearing is specified. The offset bend or protuberance prevents the rim from running up against a bearing cover disk of the roller bearing as well as preventing wear to it. The offset bend or protuberance makes a volume of material available that can decrease over the service life of the pump unit as a result of wear. This prevents damage to the needle bearing or roller bearing.